<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>postMessage</title>
    </head>
    <body>
        <textarea name="" id="" cols="30" rows="10"></textarea>
        <input type="button" value="发送">
        <iframe 
            src="http://localhost:4000/target.html" 
            frameborder="0"
            id="frame"
            onload="load()">  
        </iframe>
        <script>
            function load() {
                let frame = document.getElementById('frame')
                frame.contentWindow.postMessage('我爱你', 'http://localhost:4000') //发送数据
                window.onmessage = function(e) { 
                console.log(e.data)
                }
            }
         </script>
    </body>
</html>